1. Field of the Invention
The present invention relates to security systems, and more specifically to security systems of the type having a fixed terminal and a portable unit that delivers a signal to the fixed terminal.
2. Description of Related Art
A conventional automobile security system is one example of a security system that has a fixed terminal and a portable unit that delivers a lock/unlock signal to the fixed terminal. In the typical automobile security system, the fixed terminal is a device for the centralized locking and unlocking of the vehicle and the portable unit is a remote control for operating the locking and unlocking device. The portable unit is designed to be carried by an authorized user (e.g., the vehicle owner), and under certain conditions delivers the lock/unlock signal to the fixed terminal in order to remotely lock or unlock the doors of the vehicle. (This description uses the term "fixed", for example in designating the locking and unlocking device on the vehicle, in a relative sense and the term should be understood with reference to the portable unit.)
The lock/unlock signal from the portable unit is generally transmitted by a carrier wave such as an electromagnetic or infrared wave, and typically includes a fixed or changing code (i.e., a code whose value depends on the number of previous transmissions). The code must be recognized as valid by the fixed terminal in order for the signal to prompt the locking or unlocking of the doors of the vehicle. While this provides some anti-theft protection, the security level of such a system against theft is still imperfect because the mere physical possession of the portable unit is generally sufficient to effect the unlocking of the vehicle. Thus, if the portable unit is lost or stolen, an ill-intentioned third party can easily use the portable unit to open the doors of the vehicle and then remove articles inside the vehicle or even steal the vehicle.
To overcome this problem, a security system can be associated with its authorized user (or users) so that only an authorized user can unlock the doors of the vehicle. For example, the system can include means for measuring a biometrical signature of an authorized user. With such a means, the security system can use a biometrical signature such as a fingerprint, the iris of the eye, or an audiometrical spectrum of the authorized user's voice to identify or authenticate a physical person. To this end, it has been proposed to use a voice recognition module in the fixed terminal of a security system to control the locking or unlocking of the vehicle upon the sound of the authorized user's voice. In such a system, the portable unit becomes superfluous and can be eliminated to produce a "hands-free" access system.
While such a system would provide some advantages over conventional security systems, there is a risk that the vehicle will be accidentally unlocked. For example, when in the vicinity of the vehicle, the authorized user could inadvertently pronounce a word or sequence of words that prompts the unlocking of the vehicle. If the user does not realize that this has happened, the user may walk away and thus inadvertently leave the vehicle unguarded with its doors unlocked.